President Obama's decision, announced Wednesday, to approve new oil and gas drilling off U.S. coasts for the first time in decades reflects a high-stakes calculation by the White House: Splitting the difference on the most contentious energy issues could help secure a bipartisan climate deal this year.

In what could represent the biggest expansion of offshore energy exploration in half a century, Obama announced that he will open the door to drilling off Virginia's coast, in other parts of the mid- and south Atlantic, in the eastern Gulf of Mexico, and in waters off Alaska. At the same time, he declared off-limits the waters off the West Coast and in Alaska's Bristol Bay, canceled four scheduled lease sales in Alaska and called for more study before allowing new lease sales in the Chukchi and Beaufort seas.

What Interior Secretary Ken Salazar called "a new direction" in energy policy amounted to an offshore political gerrymander in which the administration barred drilling near states where it remains unpopular -- California and New Jersey -- and allowed it in places where it has significant support, such as Virginia and parts of Alaska and the Southeast.

Some conservative critics questioned whether the policy will have any real impact on energy production, while liberals decried the risks to the environment. But the White House's key audience -- undecided senators who will determine whether a climate bill succeeds on Capitol Hill this year -- suggested that the move had helped revive the legislation's prospects.

A string of senators, including Alaska's Mark Begich (D) and Lisa Murkowski (R), Louisiana's Mary Landrieu (D), New Hampshire's Judd Gregg (R), and Virginia Democrats Mark Warner and James Webb, praised the strategy. They have urged the administration to use a climate bill to help boost domestic energy production, through expansion of oil and gas drilling and nuclear power, and Begich and Gregg said Wednesday's announcement made them more optimistic about a deal on the bill than they have been in months.

Noting that Obama has also offered recent support for more nuclear production, Gregg said such moves show that the administration is "genuinely trying to approach the energy production issue in a multifaceted way and a realistic way, rather than listening to people on their left."

Landrieu concurred, saying that Obama is "sending as clear a signal as possible that he is willing to compromise in a way that will bring forth a great energy and climate bill, and he wants Republicans to be a part of it."

But coastal lawmakers such as Democratic Sens. Benjamin L. Cardin and Barbara A. Mikulski of Maryland joined environmentalists in blasting the change as unnecessary, and said it could jeopardize fisheries and tourist attractions.

Wooing proponents of drilling "cuts both ways," Cardin warned. "You can lose support if you do things that have environmental risks."

Many Republicans also criticized the decision, calling it halfhearted, and business groups such as the U.S. Chamber of Commerce said the administration didn't go far enough.

Nationwide, a solid majority of Americans support broader energy exploration: In the latest national survey on the subject, 63 percent of Americans told Pew pollsters in February that they favor allowing more offshore oil and gas drilling in U.S. waters.

Obama emphasized Wednesday that the policy fits within his overall framework for clean-energy development. The nation will "need to harness traditional sources of fuel even as we ramp up production of new sources of renewable, homegrown energy," he said at Joint Base Andrews Naval Air Facility Washington, formerly Andrews Air Force Base. "So today we're announcing the expansion of offshore oil and gas exploration -- but in ways that balance the need to harness domestic energy resources and the need to protect America's natural resources."

"The administration realizes, and the proponents of Kerry-Graham-Lieberman realize, they're going to have to do different and specific things for each of the 15 or so senators that remain on the fence," Freed said.

One senior Obama adviser who spoke on the condition of anonymity said it was "very, very encouraging" to hear the response on Capitol Hill to the drilling announcement. But the aide added: "We're not negotiating with people on legislation. We're letting the senators drive that process."

Many oil executives cheered the prospect of new drilling, especially in the Gulf of Mexico, where the industry is already well acquainted with the petroleum geology. The news gave a boost to companies that provide offshore drilling rigs. On a day when the stock market declined overall, shares of Diamond Offshore rose 3.98 percent, Transocean was up 3.86 percent, and Rowan increased 3.45 percent.

While the administration canceled four lease auctions that had been planned under the Bush administration, it affirmed $2 billion in Alaskan offshore leases that were sold in 2008 to Shell, ConocoPhillips, ENI and Statoil and that have been the subject of litigation.